Correct Answer: 6, 4, 2, 5, 1, 3

Solution : Given:
1. Diamond 2. Dialogue 3. Dictator 4. Dialect 5. Diameter 6. Diagram

Step 1: All the words start with the same letter D and the second letter is also the same i , move on to the next letter.
Step 2: The third letter of each word is either a or c . Based on the alphabetical order of these letters, we can arrange them – (Di a mond, Di a logue, Di a lect, Di a meter, Di a gram) and Di c tator.
Step 3: Compare the fourth letter of (Dia m ond, Dia l ogue, Dia l ect, Dia m eter, Dia g ram). Based on the alphabetical order of these letters, the order is – Diagram, (Dialogue, Dialect), and (Diamond and Diameter).
Step 4: Compare the fifth letter of (Dial o gue, Dial e ct), and (Diam o nd, Diam e ter). Dialect will come before Dialogue in the sequence as e comes before o in the alphabetical system. Similarly, Diameter will come Diamond in the sequence as e comes before o in the alphabetical system.

So, the sequence is Diagram, Dialect, Dialogue, Diameter, Diamond, or 6, 4, 2, 5, 1, 3. Hence, the fourth option is correct.